The invention relates in general to the manufacture of fiber reinforced resin composite ducts and, more particularly, to an improved method for manufacturing such ducts with integrally formed upstanding ribs.
Ducts of various shapes are widely used in aerospace and other applications. Often it is necessary that the ducts combine the lightest possible weight with high strength. This may be accomplished by forming the tubular duct and adding appropriately spaced external reinforcing ribs. With metal ducts, the ribs are generally applied by welding or riveting the ribs to the structure, methods that are time consuming, require considerable skill and generally add undesirable weight to the structure.
Recently, ducts formed from high strength fibers imbedded in a plastic resin matrix have come into use due to their high strength to weight ratio. Typical of filament winding processes are those described by Bluck in U.S. Pat. No. 3,210,228 and Carter in U.S. Pat. No. 3,303,079.
Simple ducts may be rapidly formed using filament winding processes where a resin impregnated fiber tow is wound around a mandrel, cured and removed. Adding reinforcing ribs to such structures has proved difficult. Generally, toroidal rib rings are formed by hand lay up, then bonded to the duct with adhesives or are co-cured with the duct, thereby requiring considerable hand work and complex tooling. Further, ducts made by these techniques often have a relative weak bond between duct and rib, requiring the use of additional material, with attendant undesirable weight increases, to assure adequate strength.
Thus, there is a continuing need for an improved method of manufacturing ribbed composite ducts having increased strength and lighter weight while permitting more rapid and efficient manufacture.